Commercial airports throughout the world have become extremely busy as air traffic has increased. Moving aircraft efficiently on the ground, first between landing and the gate or other landing facility to discharge passengers and cargo and then from the gate to the runway for take off, can pose challenges. Most aircraft currently require external tow vehicles or tugs to move them into or out of a gate or other landing facility. The aircraft's jet engines may also be used to help move the aircraft into or away from a gate. Both of these methods, while useful for moving aircraft, have disadvantages. Tow vehicles may not always be available for all aircraft when needed, especially when air traffic is heavy. The lack of availability of a tug or tow vehicle has the potential to delay significantly the aircraft's arrival at or departure from a gate. Waiting during such delays can be especially frustrating for passengers and crew. It is possible to back an aircraft away from a gate using the engine's reverse, thrust. This process is generally discouraged, however, because reverse thrust engine operation picks up foreign object debris (FOD) and directs FOD from the engine toward the gate, airport terminal, and everything in between. If an aircraft's main jet engines are used to move it into the gate or on the ground, fuel consumption, engine emissions, and noise are significant concerns. Moreover, engine maintenance demands for this type of aircraft ground movement tend to be high.
The aforementioned disadvantages can be overcome by providing apparatus for moving an aircraft on the ground between landing and takeoff that does not require the use of the aircraft's engines or external tow vehicles, but employs structure integral to the aircraft that enables the aircraft to be driven while on the ground. An example of such an apparatus is described in commonly owned published U.S. Patent Application No. US/2009/0261197 to Cox et al. The aircraft is effectively driven between landing and takeoff by one or more powered, self-propelled wheels without use of the aircraft's engines or assistance from tugs, tow vehicles, or the like.
Control of the ground movement of an aircraft using a powered or self-propelled wheel effectively addresses the problems arising from the use of presently available systems that are not independently driven. It is desirable, however, to be able to control the actuation of the wheel system that independently propels the aircraft to ensure that this system is activated and functional only when the aircraft is on the ground between landing and takeoff and, in addition, is operating safely. A failsafe system that prevents activation of the aircraft ground movement system and deactivates the aircraft ground movement system when the ground movement system should not be activated or cannot function safely to control aircraft ground movement is particularly desirable.
Backup control and failsafe systems for aircraft functions are known. Published U.S. Patent Applications Nos. US/2009/0177338 to Henderson et al and US/2008/0291592 to Zols, for example, respectively disclose an airplane electrical control system including redundancy to prevent loss of sensor information and a circuit breaker system useful in an aircraft on-board power system that provides current if the main current path is interrupted. In U.S. Pat. No. 7,622,818, Ausman et al provide a backup circuit that guarantees power delivery to the aircraft in case of failure of a computer-controlled switch and provides an indication to the pilot that the backup circuit is engaged. Stonestreet, II et al describe a dedicated power control and distribution system connected to an aircraft electric power supply useful for controlling a de-icing system in U.S. Pat. No. 7,355,302. A failsafe monitor senses and analyzes temperature, current, and other parameters, relating primarily to de-icing operations to ensure effective operation of the system. None of these disclosures suggests that the control systems or circuits described therein could be used in connection with a powered wheel or an aircraft ground movement system to ensure the safe operation of such a system.
U.S. Pat. No. 6,671,588 to Otake et al describes several embodiments of a system and method for controlling travel direction of an aircraft using automatic differential braking to produce changes in direction after landing and before takeoff. This system prevents malfunction of the braking mechanism when the aircraft is changing direction. Braking of the landing gear wheels may be achieved by the operation of a single brake pedal that communicates with the engine throttle control and applies a braking force depending on information received from a detector able to detect the operation state of a pilot control stick. Throttle opening and speed are judged to determine if the aircraft is in condition for flight. Very safe braking of the aircraft is possible because a failsafe arrangement prevents erroneous operation of the throttle position sensor by referring to the engine manifold pressure value and the throttle opening value to judge whether or not the airplane has landed. Otake et al, however, is notable for the absence of any suggestion that the multiple embodiments of the travel direction control system disclosed therein could be employed to ensure the safe operation of a powered aircraft wheel ground movement system.
Sibre, in U.S. Pat. No. 7,344,207, describes an apparatus used to prevent untimely braking in an aircraft electromechanical braking circuit that is controlled by a power switch under the control of a logic circuit. The switch is open by default in a no power condition and closed by a braking confirmation signal that can be a normal mode active braking signal, an emergency mode in which the braking signal is absent, and a parking mode confirmed by a parking signal. A powered failsafe brake is provided to lock the main brake actuators in a parking position, which can be maintained when the power supply to the failsafe brake is switched off. There is no suggestion in Sibre that the control or logic circuits disclosed to be effective in providing failsafe braking could be used in connection with any other aircraft functions.
A failsafe useful for protecting an aircraft engine in the event that the engine electronic control system malfunctions is disclosed in U.S. Pat. No. 4,718,229 to Riley. The control system is monitored, primarily for engine overspeed, fuel flow and temperature, and a failsafe mode is activated if a predetermined limit of the monitored parameter is exceeded. Another failsafe useful in an aircraft is described in U.S. Pat. No. 6,659,398 to Serven. This failsafe uses a two brake torque limiting device on a drive shaft line that may include an electromagnetic failsafe brake to ensure that flaps on an airplane wing are positioned to reduce asymmetry. While the systems described by Riley and Serven may be especially useful for providing failsafe operations in connection with aircraft fuel control or compensating for asymmetries in flaps and slats on an airplane wing, neither suggests that the particular failsafe described therein could be adapted to ensure the safe operation of other aircraft components and functions.
The prior art, therefore, does not disclose a failsafe system and method useful for controlling and ensuring control of the safe operation of a powered aircraft drive wheel in an aircraft ground movement system.